The present invention relates to a high-frequency amplifier circuit and a radio communication apparatus using the same.
A radio communication apparatus, for example, a portable type radio communication apparatus typified by a portable telephone powered by a battery, requires a highly efficient high-frequency power amplifier in a transmitting system thereof to enable a long communication by the battery. Thus, various techniques have increased the efficiency of the high-frequency power amplifier.
On the other hand, a communication system such as CDMA (Code Division Multiple Access) controls the transmission output of a terminal over a very wide range, and therefore requires a power amplifier that is highly efficient over a wide output power range. However, although an ordinary power amplifier has a high efficiency around a maximum output power, the ordinary power amplifier often does not have a very high efficiency at the times of medium and low output power. This is because the efficiency at the times of medium and low output power can be improved by reducing bias current, but when the bias current is reduced too much, a specification regarding distortion at the time of high output power, for example, an adjacent-channel leakage power ratio, is not met.
The following three methods are conceivable as methods for improving the efficiency at the times of medium and low output power:
(A) To reduce the bias current at the time of no signal input as much as possible. However, when the value of the current is reduced too much, a great distortion occurs at the time of high output power, and therefore specifications regarding distortion (for example, the adjacent-channel leakage power ratio) cannot be met;
(B) To control the bias current of a control electrode of an amplifying device forming the power amplifier. Specifically, the bias current is reduced at the times of medium and low output power, and the bias current is increased at the time of high output power; and
(C) To control the supply voltage of the power amplifier. Specifically, the supply voltage is reduced at the times of medium and low output power, and the supply voltage is increased at the time of high output power.
Letting Po be the high-frequency output power, Pi be input power, Ib be the direct-current bias current, and Vdd be the supply voltage, the power adding efficiency xcex7 of the power amplifier is given by the following equation:
xcex7=(Poxe2x88x92Pi)/(Ibxc3x97Vdd)xe2x80x83xe2x80x83(1)
As is clear from the equation (1), the foregoing method (B) dynamically controls the direct-current bias current Ib of the denominator to increase thereby the efficiency, whereas the forgoing method (C) dynamically controls the supply voltage Vdd of the denominator to increase thereby the efficiency.
Known as the method (C), or a conventional technique for improving the efficiency at the times of medium and low output power by controlling the supply voltage supplied to the power amplifier, is a linear transmission apparatus described in Japanese Patent Laid-Open No. Hei 3-276912, for example. The linear transmission apparatus achieves high efficiency at the times of medium and low output power by controlling the supply voltage supplied to the power amplifier by the envelope signal level of an input modulated wave and controlling an input signal of the power amplifier by the difference between the envelope signal level of the input modulated wave and the envelope signal level of an output signal of the power amplifier.
However, since the conventional technique controls the supply voltage supplied to the power amplifier by analog signal processing, the conventional technique has a problem in that the characteristics with respect to temperature and device variations are degraded It is to be noted that in part of the embodiments of the conventional technique, a digital circuit is included in a control unit but not included in the power amplifier module, and a control signal is generated by a digital baseband unit for modulating a transmission signal; therefore, a current radio communication apparatus cannot obtain the effect of increasing the efficiency at the times of medium and low output power by replacing only the power amplifier module. Incidentally, it is generally difficult to change the specifications of a digital baseband IC afterward.
In addition, when the digital baseband unit controls the supply voltage supplied to the power amplifier, the characteristics of the power amplifier with respect to the supply voltage need to be prestored in the digital baseband unit. It is therefore very inconvenient when only the power amplifier is replaced, for example. Furthermore, in reality, it is rather difficult to know the characteristics of a power amplifier to be used in advance at the time of the manufacturing of a digital baseband unit.
The present invention has been made in view of the above problems, and it is accordingly an object of the present invention to provide a high-frequency amplifier circuit and a radio communication apparatus using the same that make it possible to realize all the control by digital processing within the power amplifier module.
According to the present invention, there is provided a high-frequency amplifier circuit comprising: a detecting means for detecting input power, an averaging means for averaging the detection output of the detecting means and outputting the averaged detection output as digital data; a DC-to-DC converting means for converting an externally supplied supply voltage into a predetermined direct-current voltage; a voltage controlling means for controlling the output voltage of the DC-to-DC converting means on the basis of the output data of the averaging means; and a power amplifier operated by the output voltage of the DC-to-DC converting means for amplifying an input signal and outputting the amplified input signal.
In the thus-comprised high-frequency amplifier circuit, the detecting means outputs an analog voltage value in accordance with the level of the input power. The analog voltage value is subjected to A/D conversion and then averaged (or averaged and then subjected to A/D conversion) by the averaging means. On the basis of data of the average value of the input power, the voltage controlling means controls the output voltage of the DC-to-DC converting means. Under this control, the DC-to-DC converting means converts the externally supplied supply voltage into a low voltage at the time of medium and low output power and into a high voltage at the time of high output power, and then supplies the low voltage and the high voltage to the power amplifier as circuit supply voltage of the power amplifier. Thus, by reducing the circuit supply voltage of the power amplifier at the times of medium and low output power consumption of a current unnecessarily flowing to the power amplifier can be controlled. Consequently, the efficiency at the times of medium and low output power is increased.